Cache prefetching in offloaded data transfer (odx)

ABSTRACT

Cache prefetching in offloaded data transfer (ODX) processes. A populate token command is received to initiate a copy offload operation. Responsive to receiving the populate token command, a cache of a data storage system in a storage area network environment is instructed to prefetch data in accordance with the populate token command and complete an offloaded read request. Responsive to determining that a write using token command is not received within a specified time duration, the prefetched data stored in the cache is evicted.

FIELD OF THE INVENTION

The present invention relates generally to the field of copy offloadoperations, and more particularly improving efficiency of copy offloadoperations during an offloaded data transfer (ODX) process using cacheprefetching.

SUMMARY

Embodiments of the present invention provide systems, methods, andcomputer program products for cache prefetching in offloaded datatransfer (ODX) processes. A populate token command is received toinitiate a copy offload operation. Responsive to receiving the populatetoken command, a cache of a data storage system in a storage areanetwork environment is instructed to prefetch data in accordance withthe populate token command and complete an offloaded read request.Responsive to determining that a write using token command is notreceived within a specified time duration, the prefetched data stored inthe cache is evicted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a computing environment, in accordance withan embodiment of the present invention;

FIG. 2 is a flowchart illustrating operational steps for cacheprefetching, in accordance with an embodiment of the present invention;

FIG. 3 is a block diagram of internal and external components of thecomputer systems of FIG. 1, in accordance with an embodiment of thepresent invention;

FIG. 4 depicts a cloud computing environment, in accordance with anembodiment of the present invention; and

FIG. 5 depicts abstraction model layers, in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

A Storage Area Network (SAN) is a network that provides block-levelnetwork access for data storage. An SAN environment includes a datastorage system composed of storage devices (e.g., disk arrays and/ortape libraries) which are accessible to servers (e.g., a host computersystem). In an SAN environment, the storage devices appear to theoperating system of the host computer system as locally attached devices(i.e., direct-attached storage). Offloaded data transfer (ODX) is a copymechanism used in an SAN environment to move or copy data from onestorage device to another storage device of the data storage systemwithout transferring the data to the host computer system.

Typically, the host computer system includes a software component, suchas a client application, which issues Small Computer System Interface(SCSI) commands to another software component, such as a copy manager. Acopy manager may be operationally coupled to a logical unit whichrepresents a portion of, one of, and/or a collection of storage devices.The host computer system can use a logical unit number (LUN) to identifylogical units for executing SCSI READ and WRITE commands. When an ODXprocess is initiated, a client application of the host computer systemsends a populate token (PT) command to a copy manager. Then, arepresentation of data (ROD) is created which identifies regions of thestorage devices that include data to be copied from a source logicalunit, and the ROD is maintained in the copy manager. After the ROD iscreated, the copy manager generates a unique handle, such as a ROD Tokenwhich includes a header that is used in subsequent processing.Subsequently, the client application sends a receive ROD tokeninformation (RRTI) command which reports about the ROD creation process.Finally, a write using token (WUT) command is received by the copymanager which instructs the source logical unit to copy the data to atarget logical unit.

In typical ODX processes, copy offload operations are performed on datathat is sequential in nature. Furthermore, copy offload operations areinterspersed with normal client application write input/output (I/O)operations. In this manner, normal client application write I/Ooperations interrupt the sequential I/O pattern of READ commands forcopy offload operations. Another factor that may impact performance ofSAN environments during ODX processes is that READ commands for copyoffload operations may result in a cache miss.

Embodiments of the present invention provide methods, systems, andcomputer program products for cache prefetching during an ODX process.Embodiments of the present invention reduce a number of cache missesduring READ commands for copy offload operations.

The descriptions of the various embodiments of the present inventionhave been presented for the purposes of illustration, but are notintended to be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing form the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

FIG. 1 is a block diagram of SAN environment 100, in accordance with anembodiment of the present invention. SAN environment 100 includes hostcomputer system 110 and data storage system 130, interconnected bynetwork 120. In an embodiment, SAN environment 100 includes one hostcomputer system 110 and one data storage system 130. In anotherembodiment, SAN environment 100 may include any number of computingdevices, similar to that of host computer system 110 and data storagesystem 130.

Host computer system 110 represents a computing platform of SANenvironment 100. Host computer system 110 may be a desktop computer,laptop computer, specialized computer server, or any other computersystem known in the art. In certain embodiments, host computer system110 may represent a computer system utilizing clustered computers andcomponents to act as a single pool of seamless resources when accessedthrough network 120. For example, such embodiments may be used in datacenter, cloud computing, SAN, wide area network (WAN), and networkattached storage (NAS) applications. In certain embodiments, hostcomputer system 110 represents virtual machines. In general, hostcomputer system 110 is representative of any electronic device, orcombination of electronic devices, capable of executing machine-readableprogram instructions, in accordance with an embodiment of the presentinvention, as described in greater detail with regard to FIG. 3. In anembodiment, host computer system 110 is implemented in various cloudcomputing environments, as described in greater detail with regard toFIGS. 4 and 5.

Network 120 can be, for example, a local area network (LAN), a wide areanetwork (WAN) such as the Internet, or a combination of the two, andinclude wired, wireless, or fiber optic connections. In general, network120 can be any combination of connections and protocols that willsupport communications between host computer system 110 and data storagesystem 130, in accordance with an embodiment of the invention.

Host computer system 110 represents a platform configured to transmitSCSI commands to storage system 130 over network 120. In one embodiment,host computer system 110 includes a client application software programwhich issues SCSI commands through a SCSI initiator to a SCSI target, asdescribed in greater detail below. In another embodiment, a user caninteract with host computer system 110 via an operating system and otherstorage management tools to configure storage devices connected to SANenvironment 100 (i.e., logical units 132 and 134).

Data storage system 130 represents a storage platform configured toreceive and execute SCSI commands which are transmitted over network130. In an embodiment, data storage system 130 includes logical units132 and 134, cache 136 and copy manager 138. In another embodiment, anynumber of logical units 132 and 134 may be implemented by data storagesystem 130. In one embodiment, logical units 132 and 134, cache 136, andcopy manager 138 may each be part of separate platforms. In general,data storage system 130 is a storage platform that includes a collectionof storage devices, which are represented as logical units 132 and 134to store data for host computer system 110.

Logical units (LU) 132 and 134 represent storage devices or applicationprograms by which a user or application (e.g., a client application ofhost computer system 110, a terminal user, or an input/output mechanism)gains access to SAN environment 100. In one embodiment, any storagedevice or application program that implements LU protocols appears as aLU in SAN environment 100. In various embodiments, a portion of, one of,and/or a collection of storage devices, such as rotating disk storagemedia and tape drive storage media can be represented by LU 132 and 134.In an exemplary embodiment, a portion of data is designated to be copiedfrom LU 132 to LU 134 in accordance with a copy offload operation issuedby host computer 110, as described in greater detail below.

Cache 136 represents a memory component that is configured to storeprefetched data during a copy offload operation, in accordance with anembodiment of the present invention. The term, “prefetch,” as usedherein, refers to transferring data from another memory location (e.g.,LU 132 and 134) to cache 136 by beginning a fetch operation for data inadvance. Stated differently, “prefetching” is loading data into atemporary storage location (i.e., cache 136) before the data is actuallyneeded for another operation, such as a cache READ. In an embodiment, ifa copy offload engine, such as copy manager 138, receives a PT oroffloaded READ request, then copy manager 138 instructs cache 136 tostart prefetching regions of a source copy location (e.g., LU 132).Storing prefetched data in cache 136 facilitates fewer cache missesduring copy offloaded READ requests to cache 136. Furthermore, dependingon how fast host computer system 110 sends the off-loaded READ requestto data storage system 130, the majority of the portion of the data tobe read would already be available in cache 136. Prefetching data inaccordance with an embodiment of the present invention avoids theoverhead associated with serving the data every time a cache miss occurswhen a read is received in response to the off-loaded READ request.

FIG. 2 is a flowchart illustrating operational steps for cacheprefetching, in accordance with an embodiment of the present invention.In an embodiment, copy manager 138 receives a PT command from hostcomputer system 110 to initiate a copy offload operation (step 202). Inanother embodiment, copy manager 138 may receive an offloaded READrequest to initiate a copy offload operation. Subsequently, copy manager138 instructs cache 136 to start prefetching data indicated by the PTcommand (step 204). As previously described, the nature of a PT commandand a copy offload mechanism allows for prefetching data that issequential. In one embodiment, step 204 may occur in parallel withoffloaded READ requests. The term “parallel” as used herein, refers to asimultaneous performance of operations or near-simultaneous performanceof operations. For example, if cache 136 begins to prefetch data whilethe offloaded READ request is undergoing completion, then cache 136 isconsidered to be prefetching the data in parallel with completing theoffloaded READ request.

In decision 206, it is determined whether a time duration for receivinga WUT command is within a specified threshold. If it is determined thata time duration exceeded a threshold for receiving a WUT command (‘yes’branch, decision 206), then the prefetched pages based on the tokeninformation are added to the top of the list of cache pages that can beevicted (step 208). For example, if a specified threshold for receivinga WUT command is set at three units of time, and more than three unitsof time have elapsed without receiving the WUT command, then theoperational steps proceed with step 208. In an embodiment, evicting theprefetched pages ensures that caching behavior for the clientapplication I/O operations are not penalized. For example, if theprefetched pages are evicted based on the token information, then cache136 will be available to handle subsequent client application I/Ooperations, whereby not penalizing caching behavior of cache 136.

If it is determined that a time duration is not exceeded for receiving aWUT command (‘no’ branch, decision 206), then the WUT command iscompleted and then acknowledged by host computer system 110 (step 210).In another embodiment, once the WUT command is completed, the prefetchedpages stored in cache 136 are evicted. For example, if a specifiedthreshold for receiving a WUT command is set at three units of time, andless than three units of time have elapsed before receiving the WUTcommand, then the operational steps proceed with step 210.

Accordingly, advantages of embodiments of the present invention enablefor overall increased performance for copy offload operations, becauseeach of the offloaded READS do not result in a cache miss. Furthermore,prefetching of the offloaded READ requests, which tend to be sequentialin nature, improves a response time of storage devices, such as rotatingdisk media. Additionally, if cache 136 is instructed to free or evictpages after a WUT command has been completed, then cache 136 frees thesepages immediately instead of waiting for the pages to arrive to the topof a least recently used (LRU) list, similar to that of normalapplication data pages.

FIG. 3 is a block diagram of internal and external components of acomputer system 300, which is representative the computer systems ofFIG. 1, in accordance with an embodiment of the present invention. Itshould be appreciated that FIG. 3 provides only an illustration of oneimplementation and does not imply any limitations with regard to theenvironments in which different embodiments may be implemented. Ingeneral, the components illustrated in FIG. 3 are representative of anyelectronic device capable of executing machine-readable programinstructions. Examples of computer systems, environments, and/orconfigurations that may be represented by the components illustrated inFIG. 3 include, but are not limited to, personal computer systems,server computer systems, thin clients, thick clients, laptop computersystems, tablet computer systems, cellular telephones (e.g., smartphones), multiprocessor systems, microprocessor-based systems, networkPCs, minicomputer systems, mainframe computer systems, and distributedcloud computing environments that include any of the above systems ordevices.

Computer system 300 includes communications fabric 302, which providesfor communications between one or more processors 304, memory 306,persistent storage 308, communications unit 312, and one or moreinput/output (I/O) interfaces 314. Communications fabric 302 can beimplemented with any architecture designed for passing data and/orcontrol information between processors (such as microprocessors,communications and network processors, etc.), system memory, peripheraldevices, and any other hardware components within a system. For example,communications fabric 302 can be implemented with one or more buses.

Memory 306 and persistent storage 308 are computer-readable storagemedia. In this embodiment, memory 306 includes random access memory(RAM) 316 and cache memory 418. In general, memory 306 can include anysuitable volatile or non-volatile computer-readable storage media.Software is stored in persistent storage 308 for execution and/or accessby one or more of the respective processors 304 via one or more memoriesof memory 306.

Persistent storage 308 may include, for example, a plurality of magnetichard disk drives. Alternatively, or in addition to magnetic hard diskdrives, persistent storage 308 can include one or more solid state harddrives, semiconductor storage devices, read-only memories (ROM),erasable programmable read-only memories (EPROM), flash memories, or anyother computer-readable storage media that is capable of storing programinstructions or digital information.

The media used by persistent storage 308 can also be removable. Forexample, a removable hard drive can be used for persistent storage 308.Other examples include optical and magnetic disks, thumb drives, andsmart cards that are inserted into a drive for transfer onto anothercomputer-readable storage medium that is also part of persistent storage308.

Communications unit 312 provides for communications with other computersystems or devices via a network (e.g., network 120). In this exemplaryembodiment, communications unit 312 includes network adapters orinterfaces such as a TCP/IP adapter cards, wireless Wi-Fi interfacecards, or 3G or 4G wireless interface cards or other wired or wirelesscommunication links. The network can comprise, for example, copperwires, optical fibers, wireless transmission, routers, firewalls,switches, gateway computers and/or edge servers. Software and data usedto practice embodiments of the present invention can be downloadedthrough communications unit 312 (e.g., via the Internet, a local areanetwork or other wide area network). From communications unit 312, thesoftware and data can be loaded onto persistent storage 308.

One or more I/O interfaces 314 allow for input and output of data withother devices that may be connected to computer system 300. For example,I/O interface 314 can provide a connection to one or more externaldevices 320, such as a keyboard, computer mouse, touch screen, virtualkeyboard, touch pad, pointing device, or other human interface devices.External devices 320 can also include portable computer-readable storagemedia such as, for example, thumb drives, portable optical or magneticdisks, and memory cards. I/O interface 314 also connects to display 322.

Display 322 provides a mechanism to display data to a user and can be,for example, a computer monitor. Display 322 can also be an incorporateddisplay and may function as a touch screen, such as a built-in displayof a tablet computer.

Referring now to FIG. 4, illustrative cloud computing environment 50 isdepicted. As shown, cloud computing environment 50 comprises one or morecloud computing nodes 10 with which local computing devices used bycloud consumers, such as, for example, personal digital assistant (PDA)or cellular telephone 54A, desktop computer 54B, laptop computer 54C,and/or automobile computer system 54N may communicate. Nodes 10 maycommunicate with one another. They may be grouped (not shown) physicallyor virtually, in one or more networks, such as Private, Community,Public, or Hybrid clouds as described hereinabove, or a combinationthereof. This allows cloud computing environment 50 to offerinfrastructure, platforms and/or software as services for which a cloudconsumer does not need to maintain resources on a local computingdevice. The types of computing devices 54A-N shown in FIG. 4 areintended to be illustrative only and that cloud computing nodes 10 andcloud computing environment 50 can communicate with any type ofcomputerized device over any type of network and/or network addressableconnection (e.g., using a web browser).

Referring now to FIG. 5, a set of functional abstraction layers providedby cloud computing environment 50 (FIG. 4) is shown. The components,layers, and functions shown in FIG. 6 are intended to be illustrativeonly and embodiments of the invention are not limited thereto. Asdepicted, the following layers and corresponding functions are provided:

Hardware and software layer 60 includes hardware and softwarecomponents. Examples of hardware components include: mainframes 61; RISC(Reduced Instruction Set Computer) architecture based servers 62;servers 63; blade servers 64; storage devices 65; and networks andnetworking components 66. In some embodiments, software componentsinclude network application server software 67 and database software 68.

Virtualization layer 70 provides an abstraction layer from which thefollowing examples of virtual entities may be provided: virtual servers71; virtual storage 72; virtual networks 73, including virtual privatenetworks; virtual applications and operating systems 74; and virtualclients 75.

In one example, management layer 80 may provide the functions describedbelow. Resource provisioning 81 provides dynamic procurement ofcomputing resources and other resources that are utilized to performtasks within the cloud computing environment. Metering and Pricing 82provide cost tracking as resources are utilized within the cloudcomputing environment, and billing or invoicing for consumption of theseresources. In one example, these resources may comprise applicationsoftware licenses. Security provides identity verification for cloudconsumers and tasks, as well as protection for data and other resources.User portal 83 provides access to the cloud computing environment forconsumers and system administrators. Service level management 84provides cloud computing resource allocation and management such thatrequired service levels are met. Service Level Agreement (SLA) planningand fulfillment 85 provide pre-arrangement for, and procurement of,cloud computing resources for which a future requirement is anticipatedin accordance with an SLA.

Workloads layer 90 provides examples of functionality for which thecloud computing environment may be utilized. Examples of workloads andfunctions which may be provided from this layer include: mapping andnavigation 91; software development and lifecycle management 92; virtualclassroom education delivery 93; data analytics processing 94;transaction processing 95; and cloud computing environment 96.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

It is understood in advance that although this disclosure includes adetailed description on cloud computing, implementation of the teachingsrecited herein are not limited to a cloud computing environment. Rather,embodiments of the present invention are capable of being implemented inconjunction with any other type of computing environment now known orlater developed.

Cloud computing is a model of service delivery for enabling convenient,on-demand network access to a shared pool of configurable computingresources (e.g. networks, network bandwidth, servers, processing,memory, storage, applications, virtual machines, and services) that canbe rapidly provisioned and released with minimal management effort orinteraction with a provider of the service. This cloud model may includeat least five characteristics, at least three service models, and atleast four deployment models.

Characteristics are as follows:

On-demand self-service: a cloud consumer can unilaterally provisioncomputing capabilities, such as server time and network storage, asneeded automatically without requiring human interaction with theservice's provider.

Broad network access: capabilities are available over a network andaccessed through standard mechanisms that promote use by heterogeneousthin or thick client platforms (e.g., mobile phones, laptops, and PDAs).

Resource pooling: the provider's computing resources are pooled to servemultiple consumers using a multi-tenant model, with different physicaland virtual resources dynamically assigned and reassigned according todemand. There is a sense of location independence in that the consumergenerally has no control or knowledge over the exact location of theprovided resources but may be able to specify location at a higher levelof abstraction (e.g., country, state, or datacenter).

Rapid elasticity: capabilities can be rapidly and elasticallyprovisioned, in some cases automatically, to quickly scale out andrapidly released to quickly scale in. To the consumer, the capabilitiesavailable for provisioning often appear to be unlimited and can bepurchased in any quantity at any time.

Measured service: cloud systems automatically control and optimizeresource use by leveraging a metering capability at some level ofabstraction appropriate to the type of service (e.g., storage,processing, bandwidth, and active user accounts). Resource usage can bemonitored, controlled, and reported providing transparency for both theprovider and consumer of the utilized service.

Service Models are as follows:

Software as a Service (SaaS): the capability provided to the consumer isto use the provider's applications running on a cloud infrastructure.The applications are accessible from various client devices through athin client interface such as a web browser (e.g., web-based e-mail).The consumer does not manage or control the underlying cloudinfrastructure including network, servers, operating systems, storage,or even individual application capabilities, with the possible exceptionof limited user-specific application configuration settings.

Platform as a Service (PaaS): the capability provided to the consumer isto deploy onto the cloud infrastructure consumer-created or acquiredapplications created using programming languages and tools supported bythe provider. The consumer does not manage or control the underlyingcloud infrastructure including networks, servers, operating systems, orstorage, but has control over the deployed applications and possiblyapplication hosting environment configurations.

Infrastructure as a Service (IaaS): the capability provided to theconsumer is to provision processing, storage, networks, and otherfundamental computing resources where the consumer is able to deploy andrun arbitrary software, which can include operating systems andapplications. The consumer does not manage or control the underlyingcloud infrastructure but has control over operating systems, storage,deployed applications, and possibly limited control of select networkingcomponents (e.g., host firewalls).

Deployment Models are as follows:

Private cloud: the cloud infrastructure is operated solely for anorganization. It may be managed by the organization or a third party andmay exist on-premises or off-premises.

Community cloud: the cloud infrastructure is shared by severalorganizations and supports a specific community that has shared concerns(e.g., mission, security requirements, policy, and complianceconsiderations). It may be managed by the organizations or a third partyand may exist on-premises or off-premises.

Public cloud: the cloud infrastructure is made available to the generalpublic or a large industry group and is owned by an organization sellingcloud services.

Hybrid cloud: the cloud infrastructure is a composition of two or moreclouds (private, community, or public) that remain unique entities butare bound together by standardized or proprietary technology thatenables data and application portability (e.g., cloud bursting forload-balancing between clouds). A cloud computing environment is serviceoriented with a focus on statelessness, low coupling, modularity, andsemantic interoperability. At the heart of cloud computing is aninfrastructure comprising a network of interconnected nodes.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The terminology used herein was chosen to best explain the principles ofthe embodiment, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

What is claimed is:
 1. A method comprising: issuing, by one or morecomputer processors, a small computer system interface command from aclient application to a copy manager that manages a data storage systemto transmit a first populate token command; receiving, by the one ormore computer processors, the first populate token command to initiate afirst copy offload operation; responsive to receiving the first populatetoken command, prefetching, by the one or more computer processors, afirst set of data in accordance with the first populate token command insequentially with completing a first copy offloaded read request;transferring, by the one or more computer processors, the first set datafrom one logical unit to another logical unit in an offloaded datatransfer process using the copy manager; responsive to determining thata first write using the first token command is not received within aspecified time duration, adding, by the one or more processors, thefirst set of prefetched data stored in cache to a list of cache pagesthat can be evicted, wherein the first set of prefetched data stored isat a top of the list of cache pages that can be evicted; evicting, bythe one or more computer processors, the first set of prefetched datastored in cache; receiving, by the one or more computer processors, asecond populate token command to initiate a second copy offloadoperation; responsive to receiving the second populate token command,prefetching, by the one or more computer processors, a second set ofdata in accordance with the second populate token command in parallelwith completing a second copy offloaded read request; responsive todetermining that a second write using the second token command isreceived within the specified time duration, completing, by the one ormore computer processors, the second write using the second tokencommand; and responsive to completing the second write using the secondtoken command, evicting, by the one or more computer processors, thesecond set of data stored in the cache, wherein the second set of datastored in the cache is not added to the list of cached pages.